Free sliding number puzzle game
Numbered tiles, one empty space, put them in order. Pick a grid and play.
The number slide puzzle is the original version of the sliding puzzle: tiles numbered from 1 upward, arranged in a square grid with one cell missing. You slide a tile into the empty cell, and you win when the numbers read in order from the top-left corner with the empty cell at the bottom-right.
Numbers make the puzzle honest. There is never any doubt where a tile belongs, so the whole difficulty is in the route, not in recognising pieces. That is also why this version is used to study search algorithms: the 3×3 board has 181,440 solvable positions, the 4×4 board more than ten trillion.
It goes by several names for the same game: number slide puzzle, sliding number puzzle, slide puzzle and sliding tile puzzle. The 4×4 version with fifteen tiles is the 15 puzzle, also spelled fifteen puzzle; the 3×3 version is the 8 puzzle. Numbers always count the tiles, not the cells.
Slide any tile that touches the empty cell into it. Tiles never lift or jump. Keep sliding until the numbers run 1, 2, 3 and so on left to right, row by row, with the empty cell in the bottom-right corner. On this page you can tap a tile, drag it, swipe, or use the arrow keys.
Work in layers and never break a finished layer. Place the top row, then the left column, and treat what is left as a smaller puzzle. The last two tiles of every row are placed together: park the higher number where the lower one belongs, the lower one below it, then slide both into place. The final 2×2 corner is solved by rotating its three tiles.
Because that arrangement is one of the unsolvable half. Exactly half of all tile arrangements can never be reached by sliding, and a solved board with 14 and 15 swapped is the classic example. A board shuffled by sliding, like every board on this page, never lands in that half; a physical puzzle that was taken apart often does.